Hormonal status and vaginal function are closely linked. Diminished reproductive hormones at menopause lead to vaginal atrophy and dryness. Menopause is often accompanied by dysesthetic vulvodynia, a pain syndrome consisting of burning and itching. Together with vulvar vestibulitis, an allodynia-like syndrome linked to early oral contraceptive use, vulvodynia represents an under-recognized but significant health problem, afflicting some 16% of the adult US female population. The etiology of these syndromes is poorly understood, although vulvar vestibulitis is associated with increased numbers of pain-sensing fibers. No animal models have been available to provide a better framework of understanding. Recently, we showed that estrogen regulates vaginal innervation in rats. Ovariectomy, which approximates human menopause, dramatically increases numbers of vaginal sensory nociceptors, as well as sympathetic and parasympathetic axons. We hypothesize that this is due to modulation of trophic factor release from vaginal tissues, and that altered innervation will influence key aspects of vaginal function, including blood flow, vascular permeability, and pain sensitivity. In aim 1 we propose to characterize the relationship between hormonal status and vaginal innervation in rats during the estrous cycle, pregnancy, and adult and juvenile hormone administration. We also determine if human vaginal innervation varies with hormonal state. Aim 2 assesses cellular mechanisms underlying axonal remodeling by determining effects of reproductive hormones on vaginal target tissue and on sensory and autonomic neurons. Aim 3 examines molecular mechanisms mediating vaginal remodeling by investigating expression and functional relevance of potential trophic factors. In aim 4, we assess the functional significance of vaginal nerve remodeling on blood flow, neurogenic inflammation and behavioral avoidance of painful stimuli. These studies are conducted using methods in cell biology, tissue culture, molecular biology, physiology, pharmacology and behavior. The findings of these experiments will provide insight into mechanisms underlying hormone-dependent remodeling of vaginal innervation, and whether altered innervation may contribute to vaginal dysfunction. Moreover, these studies will provide a better understanding of the relationship between vaginal nerve plasticity and vulvodynia, and potentially lead to new therapeuties aimed at reversing vaginal sensory hyperinnervation.